Folding bicycle comprising a frame with a front frame portion on which is mounted a front wheel (1) and a rear frame portion (A) on which is mounted a rear wheel (2). The front frame portion includes an upper bar (10), a seat bar (5) and an oblique bar. The rear frame portion comprises at least one seat stay (8), at least one lower bar (9) and the seat bar (5). The oblique bar comprises an upper oblique rod (14) and a lower oblique rod (15). The lower oblique rod (15), the upper oblique rod (14), the upper bar (10) and the seat bar (5) are interconnected by joints (P1, P2, P3, P4), in this order, so as to form an articulated quadrilateral (D) deformable between a folded position and an unfolded position.